human stressors

This is my third blog covering EPA’s development of Aquatic Conservation Focus Areas for Missouri, performed in partnership with the Missouri Resource Assessment Partnership (MoRAP) back in 2006. Excitingly enough, these areas are now being used by the Missouri Department of Conservation and other organizations around the state to help them plan and implement strategies that best protect Missouri’s most vital aquatic ecosystems (see figure below). The fact that this work isn’t just sitting on the shelf is something our assessment team is proud of and is the reason I wanted to write a series of blogs highlighting it.

In the previous two blogs I laid out what we were attempting to achieve with each component of the assessment’s conservation strategy and I described the planning and assessment units we used. For this blog I will cover the methods we used to quantify human stressors at the different levels of the aquatic classification hierarchy. Obviously, human activity affects the ecological integrity of freshwater ecosystems, so this was an important part of the analysis. But this got me thinking about my own personal connection to streams and the vital riparian environments that surround them.

Urban Kansas City is where I grew up, but Missouri’s beautiful Ozark Highlands region is where my family camped in summer. Since my parents were school teachers and had summers off, I probably spent more time exploring the wilds than the average city kid. The cold clear waters of the Ozarks streams and the woods around them were my play places and where I learned to love nature. Eventually this love and appreciation led to studies and career in environmental science and to my position as Ecologist at EPA. It undoubtedly also influenced my decision to purchase land in Missouri with the specific desire of owning stream-front property. I now own 30 acres of rolling grassland with a headwater stream.

Since something like 93% of all land in Missouri is privately owned, what people do with, or on, their land is of great concern in the conservation arena. I ask myself all the time how I can help mitigate the stress continually brought to streams within this stream’s watershed, which has rolling hayfield hills and lots of grazing. It stresses me to know that in the process of trying to help the situation (i.e., converting my fescue to native grass and therefore helping native wildlife), I probably have also compromised the health of the stream. I had herbicide applied several times during dry periods and never close to my ponds or headwater – as spraying rules dictate – but I cannot be entirely sure there weren’t negative impacts in some shape or form.

Agricultural impacts, including the use of pesticides, were incorporated into our development of a Human Stressor Index (HSI), work predominantly performed by MoRAP. Working in consultation with a team of aquatic resource professionals, MoRAP generated a list of the principal human activities (stressors) known to negatively affect streams, and from it assembled the highest resolution and most recent geospatial datasets for each. Stressor statistics were developed for each of the 542 Aquatic Ecological System (AES) polygons in Missouri and correlation analysis was used to reduce this overall set of metrics into a final set of 11 relatively uncorrelated measures of human disturbance. The table below lists these along with relativized rankings developed for each. A rank of 1 means a relative low disturbance level while 4 is relatively high.

The HSI value derived for each AES is made up of three numbers: The first number reflects the highest ranking across all 11 metrics and the last two numbers reflect the sum of the 11 metrics ranging from 11 to 44, so it allows us to evaluate both individual and cumulative effects of the various stressors at the same time. For example, a value of 418 indicates relatively low cumulative impacts (i.e., last two digits = 18 out of a possible 44), however, the first number of 4 indicates that one of the stressors is relatively high and potentially acting as a major human disturbance within that AES.

Note: Taken from MORAP report (EPA definition of CAFOs uses concentrated not confined)

The map below shows the composite HSI values for each AES in Missouri. As you can see, south central Missouri shows the least human impacts, which is where I grew up during the summer months – lucky me!

Much more went into the human stressor index development than what I’ve mentioned here, such as how exactly professional knowledge was used to assign weightings and rankings, but I’ve gotten at the main gist of it for now. Most importantly, this information was incorporated into the larger analysis made up of several more components such as the percentage of public lands in an AES, or the amount of target species present. All of this will be covered in my next blog. Stay tuned for that one next month. In the mean time, let’s not get too stressed out people!

About the Author: Holly Mehl is an ecologist for EPA Region 7 who helps with water monitoring in the field and performs mapping for EPA Region 7’s program offices when in the office.

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